This application relates to a system which monitors damage to fan blades in a gas turbine engine, and reduces the power of the associated engines to increase the chance of survivability of an engine that has a damaged fan blade.
Aircraft gas turbine engines have a fan at a forward edge supplying air into a compressor section. The air is compressed and delivered downstream to a combustion section. In the combustion section, the air is mixed with fuel and burned. Products of the combustion pass downstream over turbine rotors, driving them to rotate.
The fan, being at the forward end of the engine, is subject to the ingestion of foreign objects. Recently, there have been high profile cases wherein large birds have been ingested into the fan section of a gas turbine engine on an aircraft. In one instance, both engines of a large jetliner were damaged to the point of failure by large bird ingestion.
Regulations place specific requirements on the operability of the gas turbine engine, even after ingestion of small to medium sized birds currently up to 2½ pounds (1.1 kg). However, these regulations have not required operability with larger birds of greater than 2½ pounds (1.1 kg); the only requirements for larger birds are that for birds up to 8 pounds, engine parts are not to pose a hazard to the aircraft after the bird is ingested.
One factor impacting on the design of gas turbine engines is a desire to increase fuel economy by decreasing weight. One way the designers of gas turbine engines have sought to reduce weight is to replace heavier, solid fan blades with hollow fan blades, hollow fan blades with titanium leading edges and solid composite blades. Maintaining survivability with such light weight fan blades is challenging, however.
In addition, there has been recent development of a gear train driven fan for gas turbine engines. This development will allow an increase in the diameter of the fan blades. Such an increase would increase the envelope exposed to ingestion in comparison to earlier engines at the same thrust.
Various monitoring systems for aircraft engines are known, and have provided some feedback to a pilot of damage to a particular engine. Engine rotor speeds, engine vibration and engine exhaust pressure are typically available but these provide only vague input regarding the damage to the fan rotor. Accordingly, in the past, there has been instances where pilots shut off the wrong engine based upon such vague feedback.